Synthetic silver halide emulsion binder

ABSTRACT

A PHOTOSENSITIVE SILVER HALIDE EMULSION WHEREIN THE EMULSION BINDER COMPRISES A VINYL AMINOALKYL ETHER POLYMER OR COPOLYMER.

United States Patent Office 3 ,799,781 Patented Mar. 26, 1974 Int. Cl.G03c 1/04 US. Cl. 96-113 28 Claims ABSTRACT OF THE DISCLOSURE Aphotosensitive silver halide emulsion wherein the emulsion bindercomprises a vinyl aminoalkyl ether polymer or copolymer.

BACKGROUND OF THE INVENTION This invention relates to photography andmore particularly, to novel photosensitive photographic elements,particularly novel photosensitive emulsions.

As a result of the known disadvantages of gelatin, in particular, itsvariable photographic properties and its fixed physical properties, forexample, its dilfusion characteristics; much effort has been expended inthe past in order to replace gelatin with a suitable synthetic colloidbinder for photographic silver halide emulsions. Many syntheticpolymeric materials have heretofore been suggested as peptizers forsilver halide emulsions, however, these have generally not functionedsatisfactorily and frequently have not fulfilled all of the basicrequirements for a photosensitive silver halide emulsion binder listedfollowing:

(l) absent (or constant) photographic activity;

(2) ability to form an adsorption layer on microcrystals of silverhalide permitting stable suspensions to be obtained;

(3) ability to form adsorption layers as described in (2) above which donot prevent growth of silver halide microcrystals during physicalripening; and

(4) solubility in water solution.

In addition, hithertofore, much emphasis has been placed on the abilityof the synthetic polymeric material to mix with gelatin, as thisproperty has been critical for employment in partial substitutionreactions with gelatin. Consequently, many synthetic polymers of theprior art have been materials which allow for the growth of silverhalide crystals only in the presence of gelatin.

Although hydrophilic polymers havingquaternary nitrogen atoms which arebonded to the polymer through ether linkages are described in the art asbeing suitable peptizers for silver halide dispersions in thepreparation of photographic emulsions, for example as shown in Perry andReynolds, US. Pat. No. 3,425,836, it has hithertofore been unknown toemploy the corresponding vinyl aminoalkyl ether polymers for thispurpose. Those skilled in the chemical arts are well aware of thesubstantial differences that exist in the chemical behavior ofN-substituted amine derivatives when compared with their quaternizedanalogs and therefore it was quite unexpected to find that the vinylaminoalkyl ether polymers of the present invention could also beemployed to replace gelatin, either partly or entirely, in photographicsilver halide emulsions.

SUMMARY OF THE INVENTION The present invention is directed to aphotosensitive silver halide emulsion wh'erein'the silver halidecrystals are disposed in a water soluble synthetic polymeric bindercomprising a film-forming polymer having in its structure repeatingunits represented by the formula:

wherein R is hydrogen, a lower alkyl group, i.e., 1-4 carbon alkylgroup, preferably methyl or ethyl, or a halogen, i.e., chloro, bromo, oriodo; R is hydrogen, a lower alkyl group, a halogen or cyano group; R isa lower alkylene, i.e. 1-4 carbon alkylene group or a lowercycloalkylene group, i.e. 3-6 carbon cycloalkylene group; and R and Reach is hydrogen, a lower alkyl or a lower cycloalkyl group; or R and/orR and/or R taken together represent the atoms necessary to complete a 3to 8-membered heterocyclic ring structure. The above-described polymersare herein designated for convenience as vinyl aminoalkyl etherpolymers.

If desired, the vinyl aminoalkyl ether polymer may comprise only aportion of the binder, the remainder constituting gelatin or a secondsynthetic polymer.

DETAILED DESCRIPTION OF THE INVENTION As indicated, the presentinvention is directed to photosensitive silver halide emulsions whereinphotosensitive silver halide crystals and disposed in a water-solublesynthetic polymeric binder comprising a film-forming vinyl aminoalkylether polymer having in its structure repeating units represented by theformula set forth above. The term film-forming is intended to designatea molecular weight sufliciently high to form a film, for example, amolecular weight comparable to that of gelatin (i.e., around 15,000).

Such polymers have been found to substantially meet all the basicrequirements for a gelatin substitute, as delineated above. Theemulsions of the present invention employing polymers having primary orsecondary amino groups are characterized by excellent latent imagestability. In addition, the emulsions of the present invention are morestable against degradation than gelatin; particularly against hydrolysisin acidic or basic media of the polymeric backbone and substituentgroups by virtue of the carbon-carbon and ether linkages of the instantpolymers. These polymers also show a resistance to the growth ofmicroorganisms.

As examples of monomers represented by the formula:

iii A wherein R R R3, R, and R have the above-indicated definitions-andwhich are contemplated as being suitable for providing the vinylaminoalkyl ether polymers menable for use in the present inventioninclude the following tiOII-maY-be-made 'ofithefollow'ingi-ethylenically-unsaturated monomers:

1 CH2=CH-O-CH2NH: (18) CHFCIFCOOH mm'nomethyl vinyl ether acrylic acid 2CH =CH-CH2CH:-NH 1 fl-aminoethyl vinyl ether J 0 0H (3) methaerylic acidCHz=CH-O-CH2CH2N(OH; Cl 9 20 t fi-(dimethylamino)ethyl vinyl ethercH,=&L- GO0H CH u-ehloroaerylic acid "'om=e o-oH,oHzom+NH-om' I a y Br-y-(niethylamino)p'ropylisopropenyl ether Y I I CH JI-COOH (5) (311103:I II III a-bromoaerylic'aeid' cm= OCH iCHNH-CH CH I CH;CH=CHC'OOH Jcrotonic acid H: fl-(ethylamino)propy1 1-butane-2-yl ether Ha =CHC 0 0HII I isoerotonie acid v (24) I C1CH=OHCOOH- v CHgCH-C, 0 C N CHzCH: I II fl'ehloroaerylie acid 25 I Br-CH-OH-COOH 2-(methylethylamino)prop-2-yll-ehloro-l-propenyl ether B 7 25 B-bromoaerylle acid (7) v c I J: 0 anonNH 011 CH OH I I (26) H H: v -v 01110 2 2 2 I I ClCH=(!l-'COOH I I Ifi-ehloromethacrylie acid 1 -2-11-bro l-bute 1 t 1 (n propy amlno)prop ymony e er I I I I I OHFOH COO CHI 8 I v Ol-CH=CHOCH2CHzCHzCHz-NHC CH|)methylwylamv I (as I I on; I 4(tert.buty1amino)-n-butyl fl-ehlorovlnylether 7 9 eth lmethae late O NH-CHCH1) y i W Br-0H=oH-0- (29) cl I oH o-ooo-cmcmom 2-(isopropylamino)cyclopropyl fl-bromovinyl ethernpmpy1..ch1omacry1ate I 10 I CHz==CH-O-CH2CH2N (30)BI'-CH='CHCOOCH-'CHa) I Y Y Pipefidine I II isopropyl-B-bromoacrylateCH=OHO+-CH:OH2CHa-N 9 E f I v "CH2: C0OCHzCHCHa) N-(v-vinyloxypropyl)pyrrolldine U v 9 I I I 4 I I I lsobutyl methacrylate CHz=CH0- N: .-OH|I 32 CHz=CHCOO--OHCH:OH v I 4-vinyloxy-1-methylpiperidine I I l i VIfl-hy-dmxyethyl 9 I Q 33) CH'a"=CH-COOCH,CHCH;OH v

CHz=CHOCHzCHz-N I I 'y-hydroxypropyl aerylate I :11, (34) -"on," I IN-[p-vinyloxyethyl]-N-eyclopropy1-N-methy t I CHz=lCOO-CH2CHCH; 14 f J.

. QH y 4 I I CH2 OH 0 O a I .4 I 5 1 z-h droxy-n-propyl methacrylate" Il-dimethylamlnoA-vinyloxyyeloheiane I 1 CHI=iCH C I I I, I I I (l5) CENI I I I I II II aeryIBI n' ide I 1 I I CH =JJO CHzCH2-I- a v I i .1 I: II" I g I OHF t i 1 1 th 1 tan N be cyanovmy my)? y] e Y'l-chloroaerylamide CH2=OHO@-I I i (37) I I lg: I

V CH -co-NH5 I 1 .t I I I,

3 may oxyquhmc ne I y-bromoaerylamide 17 v l I CHz=CH0C HzCHz-I i b (38)EH, v

N-[fl-(vinyloxy)ethyl] morpholine I 7 C v I I v I methacrylamide Theinstant polymers may be homopolymers or inter- OI (39) I CHzGH! polymershaving, in addition to the repeating units defined 7 I s CH -0 o-NH,-above, any compatible repeating unit or various repeatingethylaerylamide units which are not detrimental to photographic silver(40) CHI I halide emulsions and which allow the resultant polymer (l; tobe soluble in water. Examples of typical eomonomers. I I C1 CH= c whi hy G e ployed in iQIming the polymers suit- I II I I fi y mqe CH1=CHOH(obtained by hydrolyz irig vinyl alcohol copolymenzed vinyl .1 ceta e)CHz=C--QO C- CHgBr Ha lsopropenyl bromoacetate oH2=en- -o o c-c om) avinyl. pivalate om=o Ham-c o o-c cm) l N-vinyl-tertiary butylcarbamateCH=CCH2C 0 O-OH1CH;

O OH ethyl-3-carboxyd-butemte u-vinylfuran Y cm=cH--coo-oH,-O

a ncryloyloxymethyl}tetrahydrofuran v CHFCHQLOHA I p-hydroxystyrene' ICH2=CHQ m-hydroxystyrene GHFCHQ' I V I H 4 o-hydroxystyrene CHFGHQ- QOHp earboxystyrene m-earbox ystyrene N-viny1-2.-pyrrolldone (106)CHr=OH-CO-NHCHzCH N-ethylacrylam lde I (107) CH-.=CHQO -NH,CH-GH.(CH:):

OOH

N-acryloylvallne 10s CHFCII-CO-NH-CH-CHr-CHa-S-CH:

0 O H N-acrylo ylmethionine 109) CHz=CI1-GO+NH-CH-+CHr-OHr-S-OH:

O-NH2 N-aeryloylmetlnonamide CHF -CO-NH CH-CH2CH2SCH3 OOHN-methacryloylmethlonlne Polymerization of the indicated monomers isachieved by conventional free radical polymerization techniques.

The following non limiting examples illustrate the preparation ofpolymers within the' scope of the present invention. The numerical ratiobefore the word copolymer in each of the followingexamples refers to themolar ratio of monomers in the,,oopolymer.

-' EXAMPLE I 1:4 copolymer of acrylamidelp vinyloxyethylpiperidine 1.0g. of' 'a crylam'ide was dissolved in 10.0 'g. of 13-vinyloxyethylpiperidine. The resultant solution was polymerized with 0.1g. ofazoisobutyronitrile under vacuum in a sealed tube at 65? C. for 72hours after initially flushing the tube with N The thus-formedpolymerwas precipitated into acetone and the precipitate was collected, washedwith acetone and vac'uu rn dried to yield a white powder soluble in l-lO and alcohol-H 1) mixtures.

EXAMPLE II 10:3 copolymer of acrylamide/fl-(dimethylaminokthyl vinylether 7.11 g. of acrylamide and 11.51 g. of p-(dimethylamino)ethyl vinyletherwere dissolved in distilled water, and then 0.05 g. of"az'oisobutyronitrile was added. The solution was polymerized in asealed tube at 65 C. overnight, precipitated into'acetone and dried toyield a white powder soluble in H O.

' EXAMPLE III 11:4 copolymer of acrylamidelfl-aminoethyl vinyl ether14.3 g. of acr'ylamideand v60.0 g. of, a solution of fl-aminoethy l;vinyl ether in xylenewere polymerized in a sealed tube under N at C.overnight with 0.15 g. of azoisobutyronitrile. The precipitated polymerwas collected washedwith xylene and acetone-.andvvacuum dried to yield awhite powder which was soluble in H 0 and alcohol. 1 I EXAMPLE IV 9:1copolymer of ethyl acrylarnide/amino ethyl vinyl ether 44.6 g. of ethylacrylamide, 4.0 g. of amino ethyl vinyl ether, 0.097 g. of 0.2% K 5 05150 cc .of H 0 and 15 cc. of ethanol were heated at 7 C, under N; for 24hours. The thus-formed polymer was isolated by precipitation intoacetone and reprec'ipitated from methanol into ether, washed and driedbnderwvacuum at 45 C. to yield a light tansolid soluble in. H 0 andalcohol.

The following general procedure may be used for preparing photographicemulsions using the above-described polymers of the instant invention asthe colloid binders.

A water-soluble silver salt, such as silver nitrate, may be reacted withat least one water-soluble halide, such as potassium, sodium, orammonium bromide, preferably together with potassium, sodium or ammoniumiodide, in an aqueous solution of the polymer. The emulsion of silverhalide thus-formed contains water-soluble salts, as a by-product of thedouble decomposition reaction, in addition to any unreacted excess ofthe initial salts. To remove these soluble materials, the emulsion maybe centrifuged and washed with distilled water to a low conductance. Theemulsion may then be redispersed in distilled water. To an aliquot ofthis emulsion may be added a known quantity of a solution of body orthickening polymer, such as polyvinyl alcohol having an averagemolecular weight of about 100,000 (commercially available from E. I. duPont de Nemours & Company, Wilmington, Del., designated Type 72-60). Asurfactant, such as dioctyl ester of sodium sulfosuccinic acid,designated Aerosol OT (commercially available from American CyanamidCompany, New York, N.Y.), may be added and the emulsion coated onto afilm base of cellulose triacetate sheet having a coating of hardenedgelatin.

Alternatively, the soluble salts may be removed by adding to theemulsion a solution of polyacid, such as 1:1 ethylenezmaleic acidcopolymer, and lowering the pH to below 5, thereby bringing aboutprecipitation of the polyacid carrying the silver halide grains alongwith the precipitate. The resulting precipitate may then be washed andresuspended by redissolving the polyacid at pH 6-7.

The emulsions may be chemically sensitized with sulfur compounds such assodium thiosulfate or thiosulfate or thiourea, with reducing substancessuch as stannous chloride; with salts of noble metals such as gold,rhodium and platinum; with amines and polyamines; with quaternaryammonium compounds such as alkyl a-picolinium bromide; and withpolyethylene glycols and derivatives thereof.

The polymers employed as the binders in the emulsions of the presentinvention may be cross-linked according to conventional procedures. Asan example, polymers containing amine groups may be cross-linked withzirconium salts under alkaline conditions.

The emulsions of the present invention may also be optically sensitizedwith cyam'ne and merocyanine dyes. Where desired, suitable antifoggants,toners, restrainers, developers, accelerators, preservatives, coatingaids, plasticizers, hardeners and/or stabilizers may be included in thecomposition of the emulsion.

The emulsions of this invention may be coated and processed according toconventional procedures of the art. They may be coated, for example,onto various types of rigid or flexible supports, such as glass, paper,metal, and polymeric films of both the synthetic type and those derivedfrom naturally occurring products. As examples of specific materialswhich may serve as supports, mention may be made of paper, aluminum,polymethacrylic acid, methyl and ethyl esters, vinylchloride polymers,polyvinyl acetal, polyamides such as nylon, polyesters such as polymericfilm derived from ethylene glycolterephthalic acid, and cellulosederivates such as cellulose acetate, triacetate, nitrate, propionate,butyrate, acetate propionate, and acetate butyrate. Suitable subcoatsmay be provided on the supports, for example a layer of gelatin, ifnecessary or desirable for adherence, as is well known in the art.

The polymers employed in the practice of the instant invention maycontain from -100 mole percent of the above-indicated repeating units.The specific amount employed may be selected by the operator dependingupon the grain particle size and habit desired.

By selecting appropriate comonomers, the instant copolymers may be madeto be compatible with all watersoluble bodying polymers. Emulsions madefrom these novel polymers, may be bodied with any water-solublepolymers, overcoming the disadvantage encountered with gelatin which isonly compatible with a very few polymers in a most limited pH range. Asexamples of specific materials Which may serve as bodying polymers aregelatin, polyvinyl alcohol, polyacrylamide, 'polyalkylacrylamides,polyvinyl pyrrolidone, polymethacrylamidoacetamide, vinylalcohol/N-vinylpyrrolidone copolymers, poly-N- ethylaziridine,poly-N-(Z-hydroxyethyl) aziridine, poly- N-(Z-cyanoethyl) aziridine,polyQS-hydroxyethyl acrylate), polyethylene imine and cellulosederivities such as hydroxyethyl cellulose, hydroxypropyl cellulose andmethyl cellulose. It has been found that using only a small amount ofone or more of the instant polymers, large amounts of photosensitivesilver halide grains may be obtained.

An emulsion made from one of these polymers of the instant invention maytherefore be bodied with a watersoluble polymer such that the polymericconstitution of the resulting emulsion comprises a relatively largepercentage of the bodying polymer.

By selecting appropriate comonomers, copolymers with selected diffusioncharacteristics may be prepared. For example, the rate diffusion ofalkali ion or a dye-developer through an emulsion comprising one of thepolymers of this invention may be modified by varying the composition ofthe polymer.

The instant polymers containing acidic comonomers may be pH fiocculatedin order to remove the soluble salts formed as a byproduct of the doubledecomposition reaction between the water-soluble silver salt and thewatersoluble halide, in addition to any unreacted excess of the initialsalts. As an example, an acid copolymer may be precipitated by loweringthe pH below 5 and then Washed and resuspended by raising the pH toabove 7.

The instant invention will be further illustrated by reference to thefollowing nonlimiting examples.

EXAMPLE V A solution of 4.15 g. of a dry 10:3 copolymer ofacrylamide/B-(dimethylamino) ethyl vinyl ether as prepared in Example Habove, in 266 ml. of distilled water was adjusted to pH 6.30 with dilutenitric acid and maintained at a temperature of 55 C. To this solution,44.0 g. of dry potassium bromide and 0.50 g. of dry potassium iodidewere added.

A solution of 55 g. of silver nitrate in 500 ml. of distilled water wasprepared. From this silver nitrate solution, ml. was rapidly added withcontinuous agitation to the polymer-halide solution and the remainderwas added over a period of 22 minutes. Thereafter, the emulsion wasripened for 30 minutes at 55 C., and then rapidly cooled to below 20 C.

EXAMPLE VI An additional emulsion was also prepared according to theprocedure of Example V, except that only 1.04 g. of theacrylamide/fi-(dimethylamino) ethyl vinyl ether copolymer was used.

EXAMPLE VII Following essentially the same procedure as set forth inExample V with A the amount of reagents (except potassium iodide, whichwas doubled), an emulsion was made employing a 1:4acrylamide/N-(p-vinyloxyethyl) piperidine copolymer, prepared generallyaccording to the procedure of Example I. Also, the silver nitrateaddition time was reduced to 5 /2 minutes and the ripening timeincreased to 46% minutes for this emulsion.

EXAMPLE VIII An emulsion employing a 11:4 acrylamide/p-aminoethyl vinylether copolymer (generally'as prepared in Example III) was madefollowing essentially the same procedure as set forth in Example IV withA the amount of all reagents, except that the silver nitrate additiontime was reduced-to 8 minutes and the ripening time increased to 46 /2minutes.

EXAMPLE IX An emulsion employing a 9:1 ethyl acrylamide/Baminoethylvinyl ether copolymer (generally as prepared in triacetate sheet 5 milsthick subcoated with 30 mg./sq/ ft. of hardened gelatin. This film soprepared was air dried, exposed on a sensitometer, and processed with aprocessing solution and an image-receiving sheet from a Polaroid Type107 Land film assembly (Polaroid Corporation, Cambridge, Mass.). Thenegative and image-receiving element were maintained in superposedposition for a predetermined processing time, after which they werestripped apart. Alternatively, the processing was eflected with aprocessing solution and an image-receiving element from a Polaroid Type42 Land film or a Polaroid Type 20C Land film. The photographiccharacteristics of the resulting positive prints were then measured byan automatic recording densitometer. The following table summarizes thedensitometer readings obtained on samples of these prints:

TABLE II Processing Silver Film time (mg/ft?) system Dm. Dmln. A D (sea)96. 1 T-20C 0. 90 0. 44 0. 40 5 138. 2 T-20O 1. 26 0. 51 0. 75 5 136. 6'l107 0. 56 0. 18 0. 38 10 97. 3 T-C 1. 32 0. 50 0. 82 10 97. 3 T-42 1.20 0. 24 0. 96 10 97. 3 T-107 0. 99 0. 14 0. 85 10 105. 9 T-20C 1. 02 0.52 0. 50 5 105. 9 T-20C 1. 44 0. 57 0. 87 15 105. 9 T-42 1. 17 0. 0. 9210 105. 9 T-107 0. 70 0. 17 0. 58 5 105. 9 T-107 0. 90 0. 18 0. 72 10135. 7 T-42 1. 26 0. 36 0. 90 10 135. 7 T-107 0. 76 0. 20 0. 56 10 78. 8T-20C 1. 17 0. 12 1. 05 15 78. 8 T-42 1. 24 0. 32 0. 92 10 78. BT-107 1. 18 0. 12 1. 06 15 Example V) was made following essentially thesame procedure as Example V with 3& the amount of reagents and with asilver nitrate addition time of 7 minutes and a ripening time of 45minutes.

EXAMPLE XI An emulsion was prepared following the procedure of ExampleV, except that gelatin was employed as the binder rather than thesynthetic polymer.

The following table summarizes the silver halide grain sizes obtained inthe emulsions prepared in the above examples.

The emulsion mixture of Example V was centrifuged and washed with waterto a low conductance and then redispersed in distilled water. To somealiquots of this emulsion were added solutions of bodying or thickeningpolymer of polyvinyl alcohol having an average molecular weight of about100,000 (commercially available from E. I. du Pont de Nemours & Company,Wilmington, Del., designated Type 72-60) at a silver to polymer ratio ofabout 1:3 or about 2:3. The remaining aliquots received no bodyingpolymer solution. A surfactant, Aerosol OT, was added and each emulsionaliquot was slot coated at various silver coverages onto a base ofcellulos 'In certain photographic applications, it may be desirable toreplace part, but not all, of the gelatin in the photosensitiveemulsion. In view of the charactertistics of these polymers describedabove, and further, in view of their compatability with gelatin insubstantially all proportions, it will be obvious that these polymersare ideally suited for such use.

The term photosensitive and other terms of similar import are hereinemployed in the generic sense to describe materials possessing physicaland chemical properties which enable them to form usable images 'whenphotoexposed by radiation actinic to silver halide.

Since certain changes may be made in the above products and processeswithout departing from the scope of the invention herein hereininvolved, it is intended that all matter contained in the abovedescription shall be inter-, preted as illustrative only and not in alimiting sense. I

What is claimed is:

1. A photosensitive silver halide emulsion wherein the emulsion bindercomprises a water-soluble film-forming polymer having in its structurerepeating units of the formula:

3. The product as defined in claim 1 wherein said polymer comprises5-100 mole percent of said repeating units.

4. The product as defined in claim 1 wherein said silver halide emulsionis a silver iodobromide emulsion.

5. The product as defined in claim 1 wherein said emulsion includes atleast one chemical sensitizing agent.

6. The product as defined in claim 1 wherein said emulsion includes atleast one optical sensitizing agent.

7. The product as defined in claim 1 wherein said polymer is ahomopolymer.

8. The product as defined in claim 1 wherein said polymer comprises acopolymer of a first monomer of the formula:

and a second ethylenically unsaturated monomer.

9. The product as defined in claim 8 wherein said first monomer isfi-aminoethyl vinyl ether.

10. The product as defined in claim 8 wherein said first monomer isN-(B-vinyloxyethyl) piperidine.

11. The product as defined in claim 8 wherein said first monomer isfi-(dimethylamino)ethyl vinyl ether.

12. The product as defined in claim 8 wherein said second monomer isacrylamide.

13. The product as defined in claim 8 wherein said second monomer isethyl acrylamide.

14. The product as defined in claim 1 which includes a bodying polymer.

15. The product as defined in claim 14 wherein said bodying polymer ispolyvinyl alcohol.

16. The product as defined in claim 14 wherein said bodying polymer ishydroxymethyl cellulose.

17. The product as defined in claim 14 wherein said bodying polymer isgelatin.

18. A method of preparing a photosensitive silver halide emulsion whichcomprises reacting a water-soluble silver salt with a water-solublehalide salt in an aqueous solution containing a water-solublefilm-forming polymer having in its structure repeating units of theformula:

wherein R is hydrogen, a lower alkyl group or a halogen; R is hydrogen,a lower alkyl group, a halogen or cyano group; R is a lower alkylene orlower cycloalkylene group, and R and R each is hydrogen, a lower alkylgrou or lower cycloalkyl group; or R and/or R and/or R taken togetherrepresent the atoms necessary to complete a 3 to 8-membered heterocyclicring structure.

19. The method as defined in claim 18 wherein said polymer comprises acopolymer of a first monomer of the formula:

and a second ethylenically unsaturated monomer.

20. The method as defined in claim 18 wherein said first monomer isfl-aminoethyl vinyl ether.

21. The method as defined in claim 18 wherein said first monomer isN-(fi-vinyloxyethyl) piperidine.

22. The method as defined in claim 18 wherein said first monomer isp-(dimethylamino) ethyl vinyl ether.

23. The method as defined in claim 18 wherein said second monomer isacrylamide.

24. The method as defined in claim 18 wherein said second monomer isethyl acrylamide.

25. The method as defined in claim 18 wherein said aqueous solutionincludes a bodying polymer.

26. The method as defined in claim 25 wherein said bodying polymer ispolyvinyl alcohol.

27. The method as defined in claim 25 wherein said bodying polymer ishydroxyethyl cellulose.

28. The method as defined in claim 25 wherein said bodying polymer isgelatin.

References Cited UNITED STATES PATENTS 3,345,346 10/ 1967 Reynolds 961143,425,836 2/1969 Perry et al. 961 14 RONALD H. SMITH, Primary ExaminerUS. Cl. X.R.

